This invention relates generally to electrical connectors for transmitting electrical signals, and more particularly, to controlling the impedance within the circuit board held in the electrical connector.
Electrical connectors are used for transferring signals, power, ground and the like, and may comprise a circuit board held within a connector. A cable end of the circuit board has solder pads to which solid wire conductors within a cable are soldered. A separable interface end of the circuit board has contact pads and is configured to extend into a housing that is attached to a motherboard or other device. The contact pads mate to spring contacts or other separable contacts within the housing. Circuit traces are formed on a surface of the circuit board to convey signals. The circuit traces extend across a central portion and into the cable and separable interface ends.
Traditionally, a single ground plane is provided in the circuit board. Characteristic impedance is calculated based on the circuit trace dimensions in the central portion. The distance between the surface and the ground plane in the circuit board is determined to satisfy impedance requirements of the circuit traces within the central portion. The cable and separable interface ends, however, may have different geometry, such as additional circuit traces, compared to the central portion and thus have different impedance. Also, when wire conductors are soldered to the solder pads of the cable end, the impedance is further changed. Therefore, while the impedance below the central portion is controlled, the impedance throughout the circuit board is not uniform.
Signal loss increases when an unbalanced or asymmetric ground environment is created within the circuit board. When transmitting at high speeds, various signal characteristics are negatively impacted, such as increasing EM interference, increasing differential insertion loss, increasing jitter, creating mismatch in the AC return path, introducing common mode energy, creating an unbalanced or common mode signal, and the like. The reduction in signal performance becomes quite noticeable at higher data rates, such as over 4 Gbps.
Therefore, a need exists to control ground impedance of a circuit board within an electrical connector that experiences changes in geometry on one or more surfaces. Certain embodiments of the present invention are intended to meet these needs and other objectives that will become apparent from the description and drawings set forth below.